Method and apparatus for diffraction-based overlay measurement

ABSTRACT

A method of overlay error measurement includes disposing a reference pattern module over a substrate. The substrate includes first and second overlay measurement patterns in first and second locations. The reference pattern module includes first and second reference patterns. The method includes creating a first overlap of the first reference pattern with the first overlay measurement pattern and a second overlap of the second reference pattern with the second overlay measurement pattern. The method further includes determining a first overlay error between the first reference pattern of the reference pattern module and the first overlay measurement pattern of the substrate and determining a second overlay error between the second reference pattern and the second overlay measurement pattern. The method also includes determining a total overlay error between the first and second overlay measurement patterns of the substrate based on the first and second overlay errors.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, reducing overlayerrors of a photo resist layout pattern and an underlying layout patternin a lithography operation has become one of the important issues.Therefore, an efficient method of precisely determining an overlay errorbetween the photo resist layout pattern and one of the underlying layoutpatterns is desirable.

BRIEF DESCRIPTION OF THE DRAWING

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B respectively illustrate a top view and a cross-sectionalview of an overlay measurement pattern to be generated by a light beamlithography system on a wafer in accordance with some embodiments of thepresent disclosure.

FIGS. 2A and 2B respectively illustrate cross-sectional views of asubstrate having two overlay measurement patterns and FIG. 2B includesan optical system for determining an overlay error between the twooverlay measurement patterns of the substrate in accordance with someembodiments of the present disclosure.

FIGS. 3A, 3B and 3C respectively illustrate a substrate having twooverlay measurement patterns with one overlay measurement pattern havingan overlay shift (drift), positive and negative first order diffractedlight intensities as a function of the overlay shift, and a differenceof the first order diffracted light intensities as a function of theoverlay shift in accordance with some embodiments of the presentdisclosure.

FIG. 4 illustrates an exemplary overlay measurement pattern inaccordance with an embodiment of the present disclosure.

FIGS. 5A, 5B, 5C, and 5D respectively illustrate a substrate having twooverlay measurement patterns, a cross-sectional view of a referencepattern module, a top view of the reference pattern module, and a and across-sectional view of the reference pattern module that placed overthe substrate in accordance with some embodiments of the presentdisclosure.

FIGS. 6A and 6B illustrate measurement systems for determining anoverlay error in accordance with some embodiments of the disclosure.

FIGS. 7A, 7B, and 7C illustrate reference pattern groups of referencepatterns in accordance with an embodiment of the present disclosure.

FIG. 8 illustrates an exemplary measurement system for determining anoverlay error in accordance with some embodiments of the disclosure.

FIG. 9 illustrates a flow diagram of an exemplary process fordetermining an overlay error in accordance with some embodiments of thedisclosure.

FIGS. 10A and 10B illustrate an apparatus for determining an overlayerror in accordance with some embodiments of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“being made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

During an integrated circuit (IC) design, a number of layout patterns ofthe IC, for different steps of IC processing, are generated. The layoutpatterns include geometric shapes corresponding to structures to befabricated on a wafer. The layout patterns may be mask layout patternsthat are projected, e.g., imaged, on the wafer to create the IC. Alithography process transfers a layout pattern of a mask to the wafersuch that etching, implantation, or other steps are applied only topredefined regions of the wafer. Multiple layout patterns may betransferred to different layers of the wafer to create the differentstructures on the wafer. Thus, a second or subsequent layout pattern maybe transferred to a second layer on the wafer when a first or previouslayout pattern exists in a different first layer of the wafer beneaththe second layer.

As described, multiple layout patterns may be transferred to differentlayers of the wafer to create the different structures on the wafer. Itis ideal that there is no overlay error between the layout patterns thatare produced on a wafer. In some embodiments, an overlay measurementpattern, e.g., a grating, is included in each layout pattern. Theoverlay measurement pattern, which may not be part of the IC circuit, isused for determining the overlay error between different layout patternsthat are disposed on the wafer. In some embodiments, the overlay errorbetween two layout patterns of a wafer is measured when the overlaymeasurement patterns of the two layout patterns overlap. The overlappedoverlay measurement patterns of the two layout patterns are irradiatedwith a beam of light, e.g., a coherent beam of light, and the overlayerror between two layout patterns is determined, e.g., calculated, basedon diffracted light that is reflected back from the overlapped overlaymeasurement patterns of the two layout patterns.

In some embodiments, a first layout pattern that includes a firstoverlay measurement pattern is imaged, e.g., projected, onto a wafer tocreate the first layout pattern and the first overlay measurementpattern in a first layer on the wafer. In some embodiments, the firstlayer is covered with a second layer and a second layout pattern thatincludes a second overlay measurement pattern is created in the secondlayer. The second layer is initially covered with a resist materiallayer and the second layout pattern that includes the second overlaymeasurement pattern is imaged onto the resist material layer on top ofthe second layer. Therefore, the second overlay measurement pattern isin the resist material layer and the resist material layer is on top ofthe second layer that is on top of the first layer, which includes thefirst overlay measurement pattern. In some other embodiments, the secondlayer does not exist and the first layer is covered with the resistmaterial layer and the second layout pattern that includes the secondoverlay measurement pattern is imaged onto the resist material layerthat is directly on top of the first layer. Therefore, the secondoverlay measurement pattern is in the resist material layer and theresist material layer is on top of the first layer, which includes thefirst overlay measurement pattern. In either case, after the resistmaterial is developed, if the first overlay measurement pattern of thefirst layer and the second overlay measurement pattern of the resistmaterial layer on top of the first layer overlap, the overlay errorbetween the first layout pattern and the second layout pattern may bemeasured. In some embodiments, when the overlay error is below athreshold, the developed resist material that includes the second layoutpattern is used in the next processing step. Otherwise, the resistmaterial is removed and a new resist layout pattern is formed withcorrected alignment in lithography process.

As noted, the overlay error may be measured when the first overlaymeasurement pattern of the first layer and the second overlaymeasurement pattern of the resist material layer overlap. In someembodiments, each one of the layout patterns includes a plurality ofoverlay measurement patterns to make sure overlap happens in at leastone location that produces a strong diffracted light that is reflectedback from the overlapped overlay measurement patterns. In someembodiments, a reference pattern module including one or more referencepatterns is disposed on the wafer. Instead of overlapping the overlaymeasurement pattern of the resist material layer with the overlaymeasurement pattern of a layer beneath the resist material layer todetermine the overlay error, the overlay error of each layer of thesubstrate, including the resist material layer, is determined withrespect to the reference pattern module. Therefore, creating an overlapbetween the overlay measurement patterns of the resist material layerand a layer beneath the resist material layer is avoided and alsocreating a plurality of overlay measurement patterns in the layoutpattern of a layer is avoided.

In some embodiments, the reference pattern module includes a liquidcrystal display (LCD) panel having a top transparent plate, a bottomtransparent plate and liquid crystal enclosed therebetween. Top andbottom electrodes are disposed on inner surfaces of the top and bottomtransparent plates to generate patterns on the LCD panel. In addition,polarizers are disposed on the top and bottom transparent plates topolarize the light with 90 degrees polarization phase shift with respectto each other.

In some embodiments, by applying a voltage between specific portions ofthe top and bottom electrodes, one or more desired reference patternsare generated in the LCD panel. In some embodiments, one or more of thegenerated desired reference patterns is the same as the overlaymeasurement pattern of the layers of the substrate. In some embodiments,by adjusting the voltage applied between the top and bottom electrodesurfaces of the liquid crystal panel, the light transmission between thetop surface and the bottom surface can be adjusted between 0.1% and0.99%. In some embodiments, a portion of the light that enters from thetop surface is diffracted by the reference pattern that is generated inthe liquid crystal panel of the reference pattern module. In someembodiments, a portion of the light that enters from the top surface isdiffracted and reflected by the reference pattern that is generated inthe liquid crystal panel of the reference pattern module.

In some embodiments, the reference pattern module is disposed over asubstrate and the substrate has a first overlay measurement pattern in afirst layer of the substrate and a second overlay measurement pattern ina resist material layer of on top of the first layer. The liquid crystalpanel of the reference pattern module may generate a reference patternoverlapping the first overlay measurement pattern of the first layer.Also, the liquid crystal panel of the reference pattern module maygenerate another reference pattern overlapping the second overlaymeasurement pattern of the resist material layer. In some embodiments,the overlay error is measured by: First, disposing the reference patternmodule over the first layer and resist material layer. Second,generating a primary reference pattern in the reference pattern modulethat overlaps the first overlay measurement pattern of the first layer.Third, generating a secondary reference pattern in the reference patternmodule that overlaps the second overlay measurement pattern of theresist material layer. Fourth, measuring a first overlay error betweenthe primary reference pattern and the first overlay measurement patternand measuring a second overlay error between the secondary referencepattern and the second overlay measurement pattern. Fifth, determiningthe overlay error between the layout pattern of the first layer and thelayout pattern of the resist material layer based on the first andsecond overlay errors. In some embodiments, the overlay error betweenthe layout pattern of the first layer and the layout pattern of theresist material layer is also determined based on the information of thereference pattern module, e.g., based on a distance between the primaryand secondary reference patterns and additionally based on an expecteddistance between the first and the second overlay measurement patterns.

FIGS. 1A and 1B respectively illustrate a top view and a cross-sectionalview of an overlay measurement pattern to be generated by a light beamlithography system on a wafer in accordance with some embodiments of thepresent disclosure. FIG. 1A shows an overlay measurement pattern 100that is extended in a Y-direction 122 with a length 117 and isdistributed in an X-direction 124 in an extent 113. The overlaymeasurement pattern 100 includes dark strips 114 and bright strips 116.In some embodiments, dark strips 114 are low reflectance portions andthe bright strips 116 are high reflectance portions when an incidentlight beam radiates the overlay measurement pattern 100.

FIG. 1B shows a cross-sectional view of the overlay measurement pattern100 that is extended in a Z-direction 136 with a height 119 and isdistributed in the X-direction 124. In some embodiments, the dark strips114 are the features of a layer (e.g., a photo resist pattern) that areremained after a lithography process is applied and the bright strips116 are the locations that are removed after the lithography process isapplied. In other embodiments, the dark patterns and the bright patternsare reversed depending on, for example, a material of the underlyinglayer. As shown in the cross-sectional view, the dark strips 114 have awidth 134, e.g., critical dimension (CD), and the overlay measurementpattern 100 has a pitch 132. In some embodiments, when a wavelength ofthe incident light beam is comparable with the width 134 and/or thepitch 132 of the overlay measurement pattern, the incident light beam isdiffracted and a portion of the incident light beam is reflected back.The diffraction of the incident light beam is described with respect toFIG. 2B.

FIGS. 2A and 2B respectively illustrate cross-sectional views of asubstrate 232 having two overlay measurement patterns 206 and 208. FIG.2B further illustrates an optical system 220 for determining an overlayerror between the two overlay measurement patterns of the substrate inaccordance with some embodiments of the present disclosure. FIG. 2Aincludes a cross-sectional view of an overlay measurement pattern 208 ina first layer 204 that is disposed on top of an underlying substrate200. In some embodiments, the overlay measurement pattern 208 along witha corresponding circuit layout pattern (not shown) is initially disposedon the underlying substrate 200 and then the first layer 204 isdisposed, e.g., epitaxially grown or deposited, over the overlaymeasurement pattern 208. In some embodiments, a second layer 202 isdisposed, e.g., epitaxially grown or deposited, over the first layer204. In some embodiments, a resist material layer 203 is deposited overthe second layer 202 and the resist material layer 203 is exposed anddeveloped to produce an overlay measurement pattern 206 along with acorresponding layout pattern (not shown) in the resist material layer203. In some embodiments, the overlay measurement patterns 206 and 208are consistent with the overlay measurement pattern 100 of FIGS. 1A and1B. Also, consistent with FIGS. 1A and 1B, the overlay measurementpatterns 206 and 208 are distributed in the X-direction to measure anoverlay error in the X-direction. In some embodiments, overlaymeasurement patterns distributed in the Y-direction are also disposed tomeasure an overlay error in the Y-direction. In some embodiments, thesecond layer 202 does not exist and the overlay measurement pattern 206is disposed on top of the first layer 204. In some embodiments, asubstrate 232 includes the underlying substrate 200 and a structureincluding the first layer 204, the second layer 202, and the resistmaterial layer 203, on top of the underlying substrate 200.

FIG. 2B shows an optical system 220 that includes one or more lightsources 226 and one or more detectors 222. FIG. 2B further shows theoverlay measurement patterns 206 and 208 and the first layer 204, thesecond layer 202, and the resist material layer 203. In some embodimentsthe light source 226 of the optical system 220 transmits, e.g.,radiates, an incident light beam 214A to the overlay measurementpatterns 206 and 208 that have an overlap in the X-direction and in theY-direction. In some embodiments, the overlay measurement patterns 206and 208 have a same pitch and the light source 226, which is a coherentlight source, has a wavelength comparable to the pitch of the overlaymeasurement patterns 206 and 208. A portion of the incident light beam214A is diffracted and reflected from the overlay measurement pattern206 and produces the negative and positive first order diffractions 210Aand 212A respectively. A remaining portion 214B of the incident lightbeam 214A passes through the overlay measurement pattern 206 and isdiffracted and reflected from the overlay measurement pattern 208 andproduces the negative and positive first order diffractions 210B and212B respectively. Thus, the first order diffractions 210 that includesthe negative first order diffractions 210A and 210B that are reflectedare detected by one detector 222 and the first order diffractions 212that includes the positive first order diffractions 212A and 212B thatare reflected are detected by another detector 222.

An analyzer module 230 shown in FIG. 2B is coupled to the optical system220. The analyzer module 230 receives corresponding signals of thedetected first order diffractions 210 and 212 and performs an analysison the corresponding signals to determine a drift, e.g., a shift,between the overlay measurement patterns 208 and 206.

In some embodiments, the first layer 204 includes the overlaymeasurement pattern 208 as a portion of a first layout pattern. Also,the resist material layer 203 that is deposited on the second layer 202includes the overlay measurement pattern 206 as a portion of the secondlayout pattern. Thus, the lateral positional difference between theoverlay measurement patterns 208 and 206 indicates the lateralpositional difference between the first layout pattern of the firstlayer 204 and the second layout pattern to be created in the secondlayer 202 using the resist material layer 203. In some embodiments, thetop overlay measurement pattern 206 and the bottom overlay measurementpattern 208 have the same pitch and the same shape such that the numberof boxes (e.g., sub-patterns of the overlay measurement pattern), thewidth of the boxes, and the distance between the boxes in the overlaymeasurement patterns 206 and 208 are the same. In some embodiments, thetop overlay measurement pattern 206 and the bottom overlay measurementpattern 208 coincide such that the boxes in the overlay measurementpatterns 206 and 208 coincide and there is no drift between the boxes ofthe top overlay measurement pattern 206 and the boxes of the bottomoverlay measurement pattern 208. In some embodiments, due to thenumerical aperture of the optical system 220, e.g., due to the numericalaperture of the detectors 222, the first order diffractions 210 and 212enter the detectors and the higher order diffractions do not enter theoptical system 220.

FIGS. 3A, 3B and 3C respectively illustrate a substrate 232 having twooverlay measurement patterns 206 and 208 with one overlay measurementpattern having an overlay shift (FIG. 3A), negative and positive firstorder diffractions 210 and 212 as a function of the overlay shift (FIG.3B), and a difference of the first order diffracted light intensities asa function of the overlay shift distance 302 (FIG. 3C) in accordancewith some embodiments of the present disclosure. FIG. 3A is consistentwith FIG. 2A with a difference that the overlay measurement pattern 206of the resist material layer 203 on top of the second layer 202 isshifted with respect to the overlay measurement pattern 208 by a shiftdistance 302 in the positive X-direction. The shift distance 302 is adistance between the center (e.g., the center of mass or the center ofthe center pattern) of the two overlay measurement patterns 206 and 208.

FIG. 3B shows light intensities of the negative and positive first orderdiffractions 210 and 212 as a function of overlay shift distance 302. Insome embodiments, FIG. 3B respectively shows the signals correspondingto the negative and positive detected first order diffractions 210 and212 that are detected by detectors 222 of the optical system 220 in FIG.2B. In some embodiments, the analyzer module 230 receives correspondingsignals of detected first order diffractions 210 and 212 and subtractsthe signal corresponding to the negative first order diffractions 210from the signal corresponding to the positive first order diffractions212 to generate an asymmetry (AS) function 320 (FIG. 3C). As shown inFIG. 3B, the signal corresponding to the negative first orderdiffraction 210 has an intensity peak in the negative region of theshift distance 302 and the signal corresponding to the positive firstorder diffraction 212 has an intensity peak in the positive region ofthe shift distance 302. Also, FIG. 3B shows that the signalscorresponding to the negative and positive detected first orderdiffractions 210 and 212 are symmetric with respect to the intensitycoordinate 304. Although the shift distance 302 is displayed as theshift between the edges of the boxes of the overlay measurement patterns206 and 208, the origin of the overlay measurement patterns 206 and 208may be defined as the center of the overlay measurement patterns 206 and208 and the shift distance 302 can be defined with respect to a shift inthe center of the overlay measurement patterns 206 and 208.

FIG. 3C shows the AS function 320 as a function of the shift distance302. Because the signals corresponding to the negative and positivedetected first order diffractions 210 and 212 are symmetric with respectto the intensity coordinate 304, the AS function 320 passes through theorigin. In some embodiments, the AS function may be written as:

${AS} = {k \cdot {\sin\lbrack {( \frac{2\pi}{P} ) \cdot (S)} \rbrack}}$where P is a pattern (grating) pitch, S is the shift distance 302, and kis determined based on the light wavelength and a layer structure (e.g.,thickness, refractive index, and absorption coefficient) of the firstlayer, the second layer, and the resist material layer. In someembodiments, when the shift distance 302 is small compared to thepattern pitch P, the AS function may be written as:

${AS} = {k \cdot ( \frac{2\pi}{P} ) \cdot (S)}$where

$K = {k \cdot ( \frac{2\pi}{P} )}$is the slope 322 of the AS function 320 at the origin in FIG. 3C.

FIG. 4 illustrates an exemplary overlay measurement pattern inaccordance with an embodiment of the present disclosure. The overlaymeasurement pattern 400 of FIG. 4 that may be used as the overlaymeasurement pattern 206 and may be produced in the resist material layer203 has four different overlay measurement patterns. In someembodiments, when the overlay measurement pattern 400 on the topcoincides with the bottom overlay measurement pattern 208, the upperright portion 402 and the lower left portion 404 of the overlaymeasurement pattern 400 respectively have an initial shift of −D and +Din the positive X-direction with respect to the bottom overlaymeasurement pattern 208. In some embodiments, the overlay measurementpattern 400 on the top is placed with an X-direction overlay error OV,e.g., overlay placement error in the X-direction, over the bottomoverlay measurement pattern 208 and thus the AS function between theupper right portion 402 and the bottom overlay measurement pattern 208becomes:

${{AS}\; 1} = {k \cdot {\sin\lbrack {( \frac{2\pi}{P} ) \cdot ( {{OV} - D} )} \rbrack}}$which is a point on the AS function 320 of FIG. 3C with a shiftS=(OV−D). The AS function between the upper right portion 402 and thebottom overlay measurement pattern 208 may be approximated asAS1=K·(OV−D), which is a point on the slope 322 of the AS function 320of FIG. 3C with the shift S=(OV−D). Also, the AS function between thelower left portion 404 and the bottom overlay measurement pattern 208becomes:

${AS2} = {k \cdot {\sin\lbrack {( \frac{2\pi}{P} ) \cdot ( {{OV} + D} )} \rbrack}}$which is a point on the AS function 320 of FIG. 3C with a shiftS=(OV+D). The AS function between the lower left portion 404 and thebottom overlay measurement pattern 208 may be approximated asAS2=K·(OV+D), which is a point on the slope 322 of the AS function 320of FIG. 3C with the shift S=(OV+D). Thus, by using the optical system220 of FIG. 2B and measuring the negative and positive detected firstorder diffractions 210 and 212, the AS function value AS1 between theupper right portion 402 of the overlay measurement pattern 400 and thebottom overlay measurement pattern 208 and the AS function value AS2between the lower left portion 404 of the overlay measurement pattern400 and the bottom overlay measurement pattern 208 can be determined andthe overlay error OV in the X-direction may be determined as:

${OV} = {D \cdot ( \frac{{AS1} + {AS2}}{{AS2} - {AS1}} )}$

In some embodiments, when the overlay measurement pattern 400 on the topcoincides with the bottom overlay measurement pattern 208, the upperleft portion 401 and the lower right portion 405 of the overlaymeasurement pattern 400 respectively have an initial shift of −D and +Din the positive Y-direction with respect to the bottom overlaymeasurement pattern 208. Thus, the overlay error in the Y-direction maysimilarly be determined.

In some embodiments and as shown in FIGS. 1A and 1B, a width 113 of eachportion of the overlay measurement pattern 400 is between 300 nm and40,000 nm. A CD of the sub-patterns, e.g., boxes, of each portion of theoverlay measurement pattern 400 is between 10 nm and 1400 nm. A pitchbetween the sub-patterns of each portion of the overlay measurementpattern 400 is between 100 nm and 1500 nm.

FIGS. 5A, 5B, 5C, and 5D respectively illustrate a substrate 232 havingtwo overlay measurement patterns 206 and 208, a cross-sectional view ofa reference pattern module, a top view of the reference pattern module,and a cross-sectional view of the reference pattern module placed overthe substrate in accordance with some embodiments of the presentdisclosure. FIG. 5A is consistent with FIG. 3A with the difference thatthe top and bottom overlay measurement patterns 206 and 208 are indifferent non-overlapping portions of the substrate. As shown, the topand bottom overlay measurement patterns 206 and 208 are in differentlocations over the underlying layer or substrate 200 that may not beadjacent to each other. As described, the overlay measurement pattern208 is part of the first layout pattern of the first layer 204 and theoverlay measurement pattern 206 is created in the resist material layer203 on top of the second layer 202 disposed over the first layer 204.Also as described, the second layer 202 does not exist in someembodiments and the resist material layer 203 is disposed on top of thefirst layer 204.

FIG. 5B is a cross-sectional view of a reference pattern module 550,which is an LCD panel 504 having a top surface 554 and a bottom surface552. In some embodiments, the LCD panel is an LCD flat panel 504 havinga plurality of pixels and each pixel is controlled by at least one thinfilm transistor (TFT). In some embodiments, a layoutgenerator-controller 520 includes a display card for generating signalthat are applied to the TFTs to turn on/off the pixels of the LCD panelto create the sub-patterns 510A and 510B, e.g., rectangular boxes, inthe LCD panel. In some embodiments, each one of the sub-patterns 510Aand 510B includes a plurality of pixels where each pixel is locatedbetween the top and bottom surfaces 554 and 552. The TFT transistors maychange the transmission of the pixels to generate the sub-patterns 510Aand 510B. In some embodiments, the dark sub-patterns 510A and 510B arelow reflectance portions and the bright boxes neighboring thesub-patterns 510A and 510B are high reflectance portions when anincident light beam radiates the reference patterns 502A and 502B. Thus,a transmission of the sub-patterns 510A and 510B may change if avoltage, e.g., signal, is applied to the TFTs that control thesub-patterns 510A and 510B. Thus, by applying the voltage between theTFT transistors of the sub-patterns 510A and 510B to generate a desiredpattern, the group of sub-patterns 510A may perform as a referencepattern 502A and the group of sub-patterns 510B may perform as areference pattern 502B. As shown in FIGS. 5B and 5C the referencepatterns 502A and 502B may not be adjacent to each other. In someembodiments, the sub-patterns 510A (e.g., boxes) of the referencepattern 502A have a width 534A and a pitch 532A and the sub-patterns510B (e.g., boxes) of the reference pattern 502B have a width 534B and apitch 532B. In some embodiments, the reference pattern module 550 isheld in with supporting fixtures 506.

The layout generator-controller 520 is coupled to the reference patternmodule 550. In some embodiments, the layout generator-controller 520generates the signals to be applied to the TFT transistors that controlthe sub-patterns 510A and 510B to generate the reference patterns 502Aand 502B of the reference pattern module 550. In some embodiments, thelayout generator-controller 520 controls a location of the referencepattern module 550 in the X-direction and/or Y-direction. In someembodiments, by turning on/off the TFT transistors, the layoutgenerator-controller 520 moves the reference patterns 502A and 502B bythe pixel resolution of the LCD panel.

In some embodiments, a distance 556 between the center (e.g., the centerof mass or the center of the center pattern) of reference patterns 502Aand the center of reference patterns 502B is fixed, known orpredetermined. In some embodiments, the distance 556 is a known expecteddistance between the center of the overlay measurement patterns 206 and208 of the substrate 232. In some embodiments, the TFT transistors areturned on and off to change the transmission of the pixels of the LCDpanel from transparent, e.g., clear, to opaque, e.g., dark.

In some embodiments and depending on characteristics of the liquidcrystal material between the top and bottom surfaces 554 and 552, byapplying a positive voltage of 5 volts to the top surface contact andapplying a ground voltage to the bottom surface contact of thesub-patterns 510A and 510B, the reference pattern module 550 exhibitsreference patterns 502A and 502B. Thus, the reference pattern module 550may not allow the light beam that perpendicularly enters from the topsurface of the sub-patterns 510A and 510B to exit the bottom surface ofthe sub-patterns 510A and 510B. In some embodiments, the positivevoltage applied to the top surface contact is reduced such that aportion of the light beam that perpendicularly enters from the topsurface of the sub-patterns 510A and 510B exists the bottom surface ofthe sub-patterns 510A and 510B. In some embodiments, a portion of thelight that enters from the top surface is diffracted and reflected bythe one or more overlay measurement patterns that are generated by thesub-patterns 510A and 510B in the reference pattern module 550.

FIG. 5C is a top view of the reference pattern module 550 and shows thereference patterns 502A and 502B generated by the layoutgenerator-controller 520 in the reference pattern module 550. In someembodiments, the sub-patterns 510A have a uniform width 534A and/or thesub-patterns 510B have a uniform width 534B and the width 534A isdifferent from the width 534B. In some embodiments, the referencepattern 502A has a uniform pitch 532A between each two neighboringsub-patterns 510A and/or the reference pattern 502B has a uniform pitch532B between each two neighboring sub-patterns 510B and the pitch 532Ais different from the pitch 532B. In some embodiments, at least one ofthe widths 534A of the sub-patterns 510A of the reference pattern 502Aand/or at least one of the widths 534B of the sub-patterns 510B of thereference pattern 502B are not the same. In some embodiments, at leastone the pitches 532A between each two neighboring sub-patterns 510A ofthe reference pattern 502A and/or one of the pitches 532B between eachtwo neighboring sub-patterns 510B of the reference pattern 502B are notthe same.

In some embodiments, the layout generator-controller 520 generates oneor more reference patterns in the reference pattern module 550 that areconsistent with the overlay measurement pattern 400 of FIG. 4. In someembodiments, the layout generator-controller 520 generates multiplereference patterns consistent with the overlay measurement pattern 400at different locations of the reference pattern module 550, such that atleast two of the reference patterns are not adjacent to each other. Insome embodiments, the reference pattern module 550 has a length 508 inthe Y-direction.

FIG. 5D is a cross-sectional view of the reference pattern module 550placed over the substrate 232. As shown, the reference pattern 502A isshifted by a shift distance 302A, e.g., an overlay error, in thenegative X-direction with respect to the overlay measurement pattern 208of the substrate 232 and thus the shift distance 302A is a negativedistance. In addition, the reference pattern 502B is shifted by a shiftdistance 302B, e.g., an overlay error, in the positive X-direction withrespect to the overlay measurement pattern 206 of the substrate 232 andthus the shift distance 302B is a positive distance. Thus, the totaloverlay shift distance (total overlay error) between the overlaymeasurement patterns 206 and 208 is the difference between the distances302A and 302B and because the distances 302A and 302B have differentpolarity the values add to each other.

In some embodiments, both of the distances 302A and 302B have the samepolarity (not shown). The total overlay shift distance (total overlayerror) between the overlay measurement patterns 206 and 208 is thedifference between the distances 302A and distance 302B and because thedistances 302A and 302B have the same polarity the values are subtractedfrom each other.

In some embodiments, the overlay measurement patterns 206 are part of afirst layout pattern and the overlay measurement patterns 208 are partof a second layout pattern. Thus, by determining, e.g., measuring, thetotal overlay error between the overlay measurement patterns 206 and208, the overlay error between the first layout pattern and the secondlayout pattern is determined.

As shown in FIG. 5D, the center-to-center distance between the referencepatterns 502A and 502B is the distance 556 and the center-to-centerdistance between the overlay measurement patterns 206 and 208 is adistance 558. Because the shift distances 302A and 302B have oppositepolarity, a difference between the distances 556 and 558 has a value,which is a sum of the absolute values of the shift distances 302A and302B.

FIGS. 6A and 6B illustrate measurement systems for determining anoverlay error in accordance with some embodiments of the disclosure.FIG. 6A shows a substrate 602, which is consistent with the substrate232 of FIG. 5A. The substrate 602 is mounted on a stage 551, and thestage 551 is coupled to and controlled by a stage controller 560. Thereference pattern module 550 is also mounted on top of and over thesurface of the substrate 602 and in parallel with the stage 551. In someembodiments, the layout generator-controller 520 moves the referencepatterns 502A and 502B to specific locations, e.g., by turning on/offthe TFT transistors, and/or the stage controller 560 moves the substrate602 such that the reference patterns 502A and 502B generated by thelayout generator-controller 520 overlap, e.g., at least partiallyoverlap, with the overlay measurement patterns 206 and 208 of thesubstrate 602. In some embodiments, the reference pattern 502A overlapswith the overlay measurement pattern 208 of the first layer 204 and thereference pattern 502B overlaps with the overlay measurement pattern 206of the resist material layer 203. By measuring a relative positionbetween the overlay measurement pattern 208 and the reference pattern502A and a relative position between the overlay measurement pattern 206and the reference pattern 502B, it is possible to measure an overlayerror between the overlay measurement pattern 206 and the overlaymeasurement pattern 208 because the distance (e.g., center-to-centerdistance) between the reference pattern 502A and the reference pattern502B is known or predetermined.

In some embodiments as shown in FIG. 6A, one of the light sources of theoptical system 220 transmits an incident light beam 514 to the overlaymeasurement patterns 208 and the reference pattern 502A that at leasthave an overlap in the X-direction. In some embodiments, the overlaymeasurement pattern 208 and the reference pattern 502A have a samepitch. A portion of the incident light beam 514 is diffracted andreflected from the reference pattern 502A and produces the negative andpositive first order diffractions that are inner portions of first orderdiffractions 542 and 546 respectively. A remaining portion of theincident light beam 514 passes through the reference pattern 502A and isdiffracted and reflected from the overlay measurement pattern 208 andproduces the negative and positive first order diffractions that areouter portions of first order diffractions 542 and 546 respectively. Thenegative and positive first order diffractions 542 and 546 that arereflected are detected by the detector 222 of the optical system 220.

FIG. 6A also shows the analyzer module 230 that is coupled to theoptical system 220. The analyzer module 230 receives correspondingsignals of the detected first order diffractions 542 and 546 andperforms an analysis on the corresponding signals to determine a firstdrift, e.g., a first overlay error, between the overlay measurementpattern 208 and the reference pattern 502A. As described, in someembodiments, the wavelength of the light beam 514 is comparable with thepitch of the reference pattern 502A and the overlay measurement patterns208. Also, in some embodiments, the wavelength of the light beam 515 iscomparable with the pitch of the reference pattern 502B and the overlaymeasurement patterns 206. Thus, when the overlay measurement patterns208 and 206 have different pitches, two different light sources of theoptical system 220 having different wavelengths are used to produce thelight beams 514 and 515. In some embodiments, when the overlaymeasurement patterns 208 and 206 have the same pitch, the same lightsource or two different light sources of the optical system 220 may beused to produce the light beams 514 and 515.

In addition, as shown in FIG. 6A, one of the light sources of theoptical system 220 transmits an incident light beam 515 to the overlaymeasurement patterns 206 and the reference pattern 502B that at leasthave an overlap in the X-direction. In some embodiments, the overlaymeasurement pattern 206 and the reference pattern 502B have a same pitchthat is not the same as the pitches of the overlay measurement pattern208 and the reference pattern 502A. A portion of the incident light beam515 is diffracted and reflected from the reference pattern 502B andproduces the negative and positive first order diffractions that areinner portions of first order diffractions 544 and 548 respectively. Aremaining portion of the incident light beam 515 passes through thereference pattern 502B and gets diffracted and reflected from theoverlay measurement pattern 206 and produces the negative and positivefirst order diffractions that are outer portions of first orderdiffractions 544 and 548 respectively. The negative and positive firstorder diffractions 544 and 548 that are reflected are detected by thedetector 222 of the optical system 220. The analyzer module 230 receivescorresponding signals of the detected first order diffractions 544 and548 and performs an analysis on the corresponding signals to determine asecond drift, e.g., a second overlay error, between the overlaymeasurement pattern 206 and the reference pattern 502B. As described, awavelength of the light beam irradiating the overlapped referencepattern 502B and the overlay measurement pattern 206 and a wavelength ofthe light beam irradiating the overlapped reference pattern 502A and theoverlay measurement pattern 208 may be comparable to the pitches of theoverlay measurement patterns 206 and 208.

In some embodiments, the layout generator-controller 520 has theinformation of the reference patterns 502A and 502B including a distancebetween the generated reference patterns 502A and 502B. In someembodiments, the overlap between the overlay measurement patterns 208and the reference pattern 502A is concurrent with the overlap betweenthe overlay measurement pattern 206 and the reference pattern 502B. Insome embodiments, the distance between the generated reference patterns502A and 502B is the expected distance between the overlay measurementpatterns 206 and 208. Thus, the analyzer module 230 may determine theoverlay error between the overlay measurement patterns 206 and 208 basedon the first and second overlay errors.

In some embodiments, the overlap between the overlay measurement pattern208 and the reference pattern 502A is not concurrent with the overlapbetween the overlay measurement pattern 206 and the reference pattern502B. In addition, the analyzer module 230 receives the distance betweenthe generated reference patterns 502A and 502B from the layoutgenerator-controller 520 and also receives the stage 551 movement fromthe stage controller 560, and receives the location of the referencepattern module 550 from the layout generator-controller 520. Thus, theanalyzer module 230 may determine the total overlay error betweenoverlay measurement patterns 206 and 208 based on the first and secondoverlay errors, the distance between the reference patterns 502A and502B, and the movement distances of the reference pattern module 550 andthe stage 551. Thus, in some embodiments, the reference patterns 502Aand 502B of the reference pattern module 550 are generated on the flyand the width and pitch of the reference patterns 502A and 502B areselected based on the width and pitch of the overlay measurementpatterns 206 and 208. In some embodiments, the pitch of the referencepatterns 502A and 502B are adjusted to increase the diffracted signalsthat are detected by the detectors. In some embodiments, the pitch ofthe reference patterns 502A and 502B are adjusted to match with thecorresponding pitch of the overlay measurement patterns 206 and 208.

FIG. 6B shows the substrate 602, which is consistent with the substrate232 of FIG. 5A. The substrate 602 is mounted on the stage 551 and thestage 551 is coupled to and controlled by the stage controller 560. Thereference pattern module 550 is mounted on top of the substrate 602 andperpendicular to the stage 551. FIG. 6B also shows a beam splitter 606that receives an incident light beam 650 and generates from the incidentlight beam 650 a first portion 652 parallel with incident light beam andsecond portion 656 perpendicular to the incident light beam. In someembodiments, the layout generator-controller 520 moves the referencepatterns 502A and 502B to specific locations, e.g., by turning on/offthe TFT transistors, and/or the stage controller 560 moves the substrate602 such that the first portion 652 of the incident light beam 650 isincident on the reference pattern 502B and the second portion 656 of theincident light beam 650 is incident on the overlay measurement patterns206.

In some embodiments, the first portion 652 of the incident light beam650 is diffracted and reflected from the reference pattern 502B andproduces the negative and positive first order diffractions 210A and212A. The second portion 656 of the incident light beam 650 isdiffracted and reflected from the overlay measurement pattern 206 andproduces the negative and positive first order diffractions 210B and212B. In some embodiments, an optical system, e.g., the beam splitter606, receives the negative and positive first order diffractions 210Aand 212A from the reference pattern 502B and also receives the negativeand positive first order diffractions 210B and 212B from the overlaymeasurement pattern 206 and combines the received diffractions andtransmits the combined diffractions 654 to the detector 222 of theoptical system 220. In some embodiments, the diffraction angles of thenegative and positive first order diffractions 210A and 212A from thereference pattern 502B are small, e.g., less than 30 degrees. Also thediffraction angles of the negative and positive first order diffractions210B and 212B from the overlay measurement pattern 206 are small. Thus,the beam splitter 606 may combine the first order diffraction patternfrom the reference pattern 502B and from the overlay measurement pattern206. In some embodiments, optical systems, e.g., objective lenses (notshown), are placed in front of the reference pattern 502B and theoverlay measurement pattern 206. The optical systems collect the firstorder diffractions and direct the first order diffractions to becombined. The negative and positive first order diffractions of thecombined diffractions 654 are detected by the detector 222 of theoptical system 220. The analyzer module 230 receives correspondingsignals of the detected first order diffractions and performs ananalysis on the corresponding signals to determine a second drift, e.g.,the second overlay error, between the overlay measurement patterns 206and the reference pattern 502B.

In some embodiments, the layout generator-controller 520 moves thereference patterns 502A and 502B to specific locations, e.g., by turningon/off the TFT transistors, and/or the stage controller 560 moves thesubstrate 602 such that the first portion 652 of the incident light beam650 is incident on the reference patterns 502A and the second portion656 of the incident light beam 650 is incident on the overlaymeasurement patterns 208. Similarly, the analyzer module 230 determinesthe first overlay error between the overlay measurement pattern 208 andthe reference pattern 502A. Also, the analyzer module 230 may determinethe total overlay error between overlay measurement patterns 206 and 208based on the first and second overlay errors, the distance between thegenerated reference patterns 502A and 502B, and the movement distancesof the reference pattern module 550 and the stage 551. In someembodiments, instead of or in addition to moving the substrate 602and/or the reference pattern module 550, the beam splitter 606 is movedright-or-left and/or up-or-down.

FIGS. 7A, 7B, and 7C illustrate reference pattern groups of referencepatterns in accordance with an embodiment of the present disclosure.FIG. 7A illustrates a reference pattern group 700 that includes a numberof reference patterns 701 that are consistent with the overlymeasurement patterns of FIG. 4 with multiple widths and pitches that arearrange along a perimeter of a substrate 710. In some embodiments, thereference patterns 701 of the reference pattern group 700 are disposedon the substrate 710 by, for example, oxide growth, patterning bylithography, and etching.

FIG. 7B illustrates a reference overlay pattern group 750 that includesa number of reference patterns 701 with multiple widths and pitches thatare arranges in a substrate 720. In some embodiments, the referencepatterns 701 of the reference pattern group 750 are disposed on thesubstrate 720 by, for example, oxide growth, patterning by lithography,and etching.

FIG. 7C is a cross-sectional view of a reference pattern module 553 thatis consistent with the reference pattern module 550 of FIG. 5B. Thereference pattern module 553 is created by disposing the sub-patterns(boxes) 513A and 513B on a substrate 555. The reference pattern module553 is not a liquid crystal panel and the sub-patterns (boxes) 513A and513B of the reference pattern module 553 are created through oxidegrowth, patterning the oxide, and etching the oxide. However, thesub-patterns (boxes) 513A and 513B are consistent with the sub-patterns(boxes) 510A and 510B and the reference patterns 503A and 503B arerespectively consistent with the reference patterns 502A and 502B. Insome embodiments, the measurement systems of FIGS. 6A and 6B may use thereference pattern module 553 instead of the reference pattern module550. Referring back to FIG. 6B, the layout position controller 521 ofFIG. 7C and/or the stage controller 560 moves the substrate 602 and/orthe reference pattern module 553 such that the first portion 652 of theincident light beam 650 is incident on a selected reference pattern 503Aof the reference pattern module 553 and the second portion 656 of theincident light beam 650 is incident on the overlay measurement patterns208. In addition, the layout position controller 521 and/or the stagecontroller 560 moves the substrate 602 and/or the reference patternmodule 553 such that the first portion 652 of the incident light beam650 is incident on the reference pattern 503B of the reference patternmodule 553 and the second portion 656 of the incident light beam 650 isincident on the overlay measurement patterns 206. In some embodiments,the reference patterns 503A and 503B are not adjacent to each other.

FIG. 8 illustrates a measurement system for determining an overlay errorin accordance with some embodiments of the disclosure. The system 800includes an analyzer module 830 and a main controller 840 coupled toeach other. The analyzer module 830, which is consistent with theanalyzer module 230 of FIGS. 2B, 6A, and 6B receives one or more layoutpatterns 810 to be generated on the reference pattern module 550 of theFIGS. 5B and 5C. The analyzer module 830 may either directly connect tothe optical system 804 or may connect to the optical system 804 via themain controller 840.

In some embodiments, the main controller 840 is coupled to a layoutgenerator 808, a layout position controller 806, an optical system 804,and a stage controller 802. In some embodiments and returning back toFIGS. 2B, 6A, and 6B the optical system 804 is consistent with theoptical system 220. The optical system 804, which is controlled by themain controller 840, generates the incident light beams 214A, 514, 515,and 650 of FIGS. 2B, 6A, and 6B. In addition, the optical system 804receives the diffracted light from the overlay measurement patterns anddetects the diffracted light and generates corresponding signals of thedetected diffracted light. The optical system 804 sends thecorresponding signals of the detected diffracted light to the analyzermodule for analysis as described above with respect to FIGS. 6A and 6Bto determine a drift between different overlay measurement patterns ofthe substrate. In some embodiments, the layout generator-controller 520of FIGS. 5B, 6A, and 6B is consistent with the combination of the layoutposition controller 806 and layout generator 808. In some embodiments,the layout position controller 521 of FIG. 7C is consistent with thelayout position controller 806. In some embodiments, the layout positioncontroller 806 is combined into the layout generator 808 and by turningon/off the TFT transistors, the layout generator 808 moves the referencepatterns by the pixel resolution of the LCD panel.

In some embodiments, the analyzer module 830 sends the one or morelayout patterns 810 directly or via the main controller 840 to thelayout generator 808 and commands the layout generator 808 to create theone or more layout patterns 810 in the reference pattern module 550 ofthe FIGS. 5B, 5C, 6A, and 6B.

FIG. 9 illustrates a flow diagram of an exemplary process 900 fordetermining an overlay error in accordance with some embodiments of thedisclosure. The process 900 may be performed by the measurement systemsof FIGS. 6A, 6B, and 8. In some embodiments, a portion of the process900 is performed and/or is controlled by the computer system 1000described below with respect to FIGS. 10A and 10B. The method includesthe operation S902 of disposing a reference pattern module that includesfirst and second reference patterns over a substrate. As shown in FIG.5B, the reference pattern module 550 includes the first and secondreference patterns 502A and 502B. Also, as shown in FIGS. 6A and 6B thereference pattern module 550 is placed above, e.g., over, a substrate602. In some embodiments, the substrate 602 includes first and secondoverlay measurement patterns 206 and 208.

In operation S904, at least a first partial overlap is created betweenthe first reference pattern and the first overlay measurement pattern ofthe substrate. As shown in FIG. 6A, an overlap is created between thefirst reference pattern 502A of the reference pattern module 550 and thefirst overlay measurement pattern 208 of the substrate 602.

In operation S906, at least a second partial overlap is created betweenthe second reference pattern and the second overlay measurement patternof the substrate. As shown in FIG. 6A, an overlap is created between thesecond reference pattern 502B of the reference pattern module 550 andthe second overlay measurement pattern 206 of the substrate 602. In someembodiments, operations S904 and S906 are performed simultaneously.

In operation S908, a first layout error between the first referencepattern and first overlay measurement patterns is determined. As shownin FIG. 6A, the optical system 220 transmits the incident light beam 514to the first reference pattern 502A that is on top of the first overlaymeasurement pattern 208. The reflected first order diffractions 542 and546 from the first reference pattern 502A and from the first overlaymeasurement pattern 208 are detected by the optical system 220 and thedetected signals are transmitted to the analyzer module 230. Theanalyzer module 230 determines, e.g., calculates, the first layout errorbetween the first overlay measurement pattern 208 and the firstreference pattern 502A based on the detected signals.

In operation S910, a second layout error between the second referencepattern and second overlay measurement patterns is determined. As shownin FIG. 6A, the optical system 220 transmits the incident light beam 515to the second reference pattern 502B that is on top of the secondoverlay measurement pattern 206. The reflected first order diffractions544 and 548 from the second reference pattern 502B and from the secondoverlay measurement pattern 206 are detected by the optical system 220and the detected signals are transmitted to the analyzer module 230. Theanalyzer module 230 calculates the second layout error between thesecond measurement patterns 206 and the second reference pattern 502Bbased on the detected signals.

In operation S912, a total layout error between the first and the secondoverlay measurement patterns of the substrate is determined. The totallayout error between the first overlay measurement pattern 208 and thesecond overlay measurement pattern 206 is determined by the analyzermodule 230. In some embodiments, as described above, the total layouterror is an algebraic sum, e.g., addition or subtraction, of the firstand the second layout errors.

FIGS. 10A and 10B illustrate an apparatus for determining an overlayerror in accordance with some embodiments of the disclosure. FIG. 10A isa schematic view of a computer system 1000 that executes the process fordetermining the overlay error according to one or more embodiments asdescribed above. All of or a part of the processes, method and/oroperations of the foregoing embodiments can be realized using computerhardware and computer programs executed thereon. The operations includecontrolling an optical system and the light sources and detectors of theoptical system, analyzing the light detected by the detectors,generating and/or controlling the generation of reference patterns in areference pattern module, and controlling the movement of a stageholding a substrate and the movement of the reference pattern module tocombine the diffracted light from the overlay measurement patterns ofthe substrate on the stage and the reference patterns of the referencepattern module. Thus, in some embodiments, the computer system 1000provides the functionality of the analyzer module 830, the maincontroller 840, the stage controller 802, the layout position controller806, and a controller of the optical system 804. In FIG. 10A, a computersystem 1000 is provided with a computer 1001 including an optical diskread only memory (e.g., CD-ROM or DVD-ROM) drive 1005 and a magneticdisk drive 1006, a keyboard 1002, a mouse 1003, and a monitor 1004.

FIG. 10B is a diagram showing an internal configuration of the computersystem 1000. In FIG. 10B, the computer 1001 is provided with, inaddition to the optical disk drive 1005 and the magnetic disk drive1006, one or more processors 1011, such as a micro-processor unit (MPU),a ROM 1012 in which a program such as a boot up program is stored, arandom access memory (RAM) 1013 that is connected to the processors 1011and in which a command of an application program is temporarily storedand a temporary storage area is provided, a hard disk 1014 in which anapplication program, a system program, and data are stored, and a bus1015 that connects the processors 1011, the ROM 1012, and the like. Notethat the computer 1001 may include a network card (not shown) forproviding a connection to a LAN.

The program for causing the computer system 1000 to execute the processfor determining an overlay error of a semiconductor device in theforegoing embodiments may be stored in an optical disk 1021 or amagnetic disk 1022, which are inserted into the optical disk drive 1005or the magnetic disk drive 1006, and transmitted to the hard disk 1014.Alternatively, the program may be transmitted via a network (not shown)to the computer 1001 and stored in the hard disk 1014. At the time ofexecution, the program is loaded into the RAM 1013. The program may beloaded from the optical disk 1021 or the magnetic disk 1022, or directlyfrom a network. The program does not necessarily have to include, forexample, an operating system (OS) or a third party program to cause thecomputer 1001 to execute the process for manufacturing the lithographicmask of a semiconductor device in the foregoing embodiments. The programmay only include a command portion to call an appropriate function(module) in a controlled mode and obtain desired results.

As discussed above, a stand-alone reference pattern module separate fromthe substrate can be used for determining an overlay error betweendifferent layout patterns of the substrate or between an existing layoutpattern of the substrate and a layout pattern of a resist material layeron the substrate that is being patterned by a lithographic process. Byusing the stand-alone reference pattern module, the overlay error ofeach layer is measured with respect to the stand-alone reference patternmodule. The overlay error of each two layers can be determined by analgebraic sum of the overlay errors between the two layers and thestand-alone reference pattern module. Therefore, the different patternedlayers of the substrate do not need to have multiple overlay measurementpatterns in each layer to make sure there is an overlap between theoverlay measurement patterns of each two layers. Also, the overlaymeasurement pattern does not need to be re-designed when the film stackchanges.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to some embodiments of the present disclosure, a method ofoverlay error measurement includes disposing a reference pattern moduleover a substrate. The substrate includes a first overlay measurementpattern in a first location and a second overlay measurement patternseparate from the first overlay measurement pattern in a secondlocation. The reference pattern module includes a first referencepattern and a second reference pattern separate from the first referencepattern. The method includes creating at least a first partial overlapof the first reference pattern with the first overlay measurementpattern under the reference pattern module and concurrently with thefirst partial overlap, creating at least a second partial overlap of thesecond reference pattern with the second overlay measurement patternunder the reference pattern module. The method further includesdetermining a first overlay error between the first reference pattern ofthe reference pattern module and the first overlay measurement patternof the substrate, determining a second overlay error between the secondreference pattern of the reference pattern module and the second overlaymeasurement pattern of the substrate, and determining a total overlayerror between the first and second overlay measurement patterns of thesubstrate based on the first and second overlay errors. In anembodiment, the first overlay measurement pattern is included in a firstlayout pattern that is in a first layer of the substrate and the secondoverlay measurement pattern is included in a second layout pattern thatis in a second layer of the substrate different from the first layer andan overlay error between the first and the second layout patterns isdetermined based on the total overlay error. In an embodiment,determining the overlay error between the first and the second layoutpatterns includes determining an algebraic sum of the first and secondoverlay errors. In an embodiment, determining the first overlay errorincludes applying a first beam of light over the first partial overlapof the first reference pattern and the first overlay measurement patternand analyzing diffracted light from the first overlay measurementpattern and the first reference pattern to determine the first overlayerror. In an embodiment, determining the second overlay error includesapplying a second beam of light over the second partial overlap of thesecond reference pattern and the second overlay measurement pattern andanalyzing diffracted light from the second overlay measurement patternand the second reference pattern to determine the second overlay error.In an embodiment, analyzing the diffracted light includes determining anintensity difference between positive and negative first orderdiffracted light. In an embodiment, the method further includes thatprior to the first partial overlap, generating the first referencepattern and the second reference pattern of the reference patternmodule. The first reference pattern has a first pitch equal to a pitchof the first overlay measurement pattern of the substrate and the secondreference pattern has a second pitch equal to a pitch of the secondoverlay measurement pattern of the substrate. In an embodiment, thefirst reference pattern of the reference pattern module includes a firstplurality of third sub-patterns extending in a first direction and beingarranged in a second direction crossing the first direction, and asecond plurality of third sub-patterns extending in the first directionand being arranged in the second direction. The first plurality of thirdsub-patterns and the second plurality of third sub-patterns are arrangedwith an equal distance D3 at opposite sides of a third central lineextending in the first direction. Also, the first overlay measurementpattern of the substrate includes a third plurality of firstsub-patterns extending in the first direction and being arranged in thesecond direction crossing the first direction, and a fourth plurality offirst sub-patterns extending in the first direction and being arrangedin the second direction. The third plurality of first sub-patterns andthe fourth plurality of first sub-patterns are arranged with an equaldistance D1 at opposite sides of a first central line extending in thefirst direction and when the first reference pattern of the referencepattern module is disposed over the first overlay measurement pattern ofthe substrate and the first central line and the third central lineoverlap, the first plurality of third sub-patterns of the firstreference pattern of the reference pattern module has an offset d=D1−D3with the third plurality of first sub-patterns of the first overlaymeasurement pattern of the substrate and the second plurality of thirdsub-patterns of the first reference pattern of the reference patternmodule has an offset −d=D3−D1 with the fourth plurality of firstsub-patterns of the first overlay measurement pattern of the substrate.In an embodiment, determining the first overlay error includes applyinga first beam of light over the first partial overlap of the firstoverlay measurement pattern and the first reference pattern. Determiningthe first overlay error also includes analyzing a first diffracted lightfrom the first plurality of third sub-patterns of the first referencepattern and the third plurality of first sub-patterns of the firstoverlay measurement pattern to determine a first asymmetry function AS1based on positive and negative first order diffraction of the firstdiffracted light. Determining the first overlay error further includesanalyzing a second diffracted light from the second plurality of thirdsub-patterns of the first reference pattern and the fourth plurality offirst sub-patterns of the first overlay measurement pattern to determinea second asymmetry function AS2 based on positive and negative firstorder diffraction of the second diffracted light. Determining the firstoverlay error further includes determining the first overlay errorbetween the first reference pattern of the reference pattern module andthe first overlay measurement pattern of the substrate as:

${d( \frac{{AS1} + {AS2}}{{AS1} - {AS2}} )}.$

According to some embodiments of the present disclosure, a method ofoverlay error measurement includes performing a first analysis of afirst combination of diffracted light received from a first referencepattern of a reference pattern module and received from a first overlaymeasurement pattern in a first location of a first layer of a substrateto determine a first overlay error between the first reference patternof the reference pattern module and the first overlay measurementpattern of the substrate. The method also includes performing a secondanalysis of a second combination of diffracted light received from asecond reference pattern of a reference pattern module and received froma second overlay measurement pattern in a second location of a secondlayer of the substrate to determine a second overlay error between thesecond reference pattern of the reference pattern module and the secondoverlay measurement pattern of the substrate. The method furtherincludes determining a total overlay error between the first and secondoverlay measurement pattern of the substrate based on the first andsecond overlay errors. In an embodiment, the reference pattern module isdisposed in parallel over the substrate. In an embodiment, the firstoverlay measurement pattern and the second overlay measurement patternare in different layers of the substrate. In an embodiment, thereference pattern module is disposed perpendicular to the substrate andthe method further includes projecting a coherent beam of light to abeam splitter and configuring the beam splitter to direct a firstportion of the coherent beam of light from the beam splitter to thefirst reference pattern of the reference pattern module and directing aremaining second portion of the coherent beam of light from the beamsplitter to the first location of the first layer of the substrate. Themethod further includes combining by the beam splitter, diffracted lightreceived from the first reference pattern of the reference patternmodule and received from the first overlay measurement pattern in thefirst location of the substrate to generate the first combination ofdiffracted light. The method also includes directing, by the beamsplitter, the first combination of diffracted light received from thefirst overlay measurement pattern and received from the first referencepattern to an optical system for detection and analysis. And the methodincludes analyzing positive and negative first order diffraction of thefirst combination of diffracted light by an analyzer module coupled toor included in the optical system to determine the first overlay error.In an embodiment, the method further includes configuring the beamsplitter to direct the first portion of the coherent beam of light fromthe beam splitter to the second reference pattern of the referencepattern module and directing the remaining second portion of thecoherent beam of light from the beam splitter to the second location ofthe second layer of the substrate. The method includes combining by thebeam splitter, diffracted light received from the second referencepattern of the reference pattern module and received from the secondoverlay measurement pattern in the second location of the substrate togenerate the second combination of diffracted light. The method includesdirecting, by the beam splitter, the second combination of diffractedlight received from the second overlay measurement pattern and receivedfrom the second reference pattern to the optical system for detectionand analysis. And the method includes analyzing positive and negativefirst order diffraction of the second combination of diffracted light bythe analyzer module to determine the second overlay error.

According to some embodiments of the present disclosure, a system fordetermining an overlay error includes a main controller and a referencepattern module disposed above a substrate, the substrate comprising afirst overlay measurement pattern in a first location of the substrateand a second overlay measurement pattern in a second location of thesubstrate. The system includes an analyzer module coupled to the maincontroller. The analyzer module receives a first reference pattern and asecond reference pattern. The system includes a layout generator coupledto the main controller and receives the first and second referencepatterns and an offset between the first and second reference patternsfrom the analyzer module via the main controller. The layout generatoris further coupled to the reference pattern module and generates thefirst and the second reference patterns in the reference pattern module.The system includes a stage controller coupled to the main controller tocontrol the movement of the substrate and an optical system thatincludes one or more light sources and coupled to the main controller.The one or more light sources generate a first beam of light to radiatethe first reference pattern of the reference pattern module and toradiate the first overlay measurement pattern of the substrate. The oneor more light sources generate a second beam of light to radiate thesecond reference pattern of the reference pattern module and to radiatethe second overlay measurement pattern of the substrate. The opticalsystem also includes one or more light detectors. The one or more lightdetectors receive a first combination of diffracted light from the firstoverlay measurement pattern and the first reference pattern and receivea second combination of diffracted light from the second overlaymeasurement pattern and the second reference pattern. The analyzermodule also receives detected signals associated with the firstcombination of diffracted light to determine a first overlay errorbetween the first reference pattern of the reference pattern module andthe first overlay measurement pattern of the substrate and receivesdetected signals associated with the second combination of diffractedlight to determine a second overlay error between the second referencepattern of the reference pattern module and the second overlaymeasurement pattern of the substrate. In an embodiment, the firstoverlay measurement pattern is included in a first layout pattern in afirst layer of the substrate and the second overlay measurement patternis included in a second layout pattern in a second layer of thesubstrate different from the first layer. An overlay error between thefirst layout pattern and the second layout pattern of the substrate isdetermined based on the first overlay error and the second overlayerror. In an embodiment, the reference pattern module is disposed inparallel over the substrate. The system further includes a layoutposition controller coupled to the reference pattern module to move thereference pattern module in parallel with the substrate. The stagecontroller and the layout position controller produce at least a firstpartial overlap of the first reference pattern above the substrate withthe first overlay measurement pattern in the first location of thesubstrate. And also produce at least a second partial overlap of thesecond reference pattern above the substrate with the second overlaymeasurement pattern in the second location of the substrate. The one ormore light sources produce the first beam of light over the firstpartial overlap and produce the second beam of light over the secondpartial overlap. In an embodiment, the reference pattern module isdisposed over the substrate and perpendicular to a surface of thesubstrate. The system further includes a layout position controllercoupled to the reference pattern module to move the layout positioncontroller perpendicular to the substrate. The system includes a beamsplitter to receive the first beam of light and to split the first beamof light such that a first portion of the first beam of light radiatesthe first overlay measurement pattern at the first location of thesubstrate and a remaining second portion of the first beam of lightradiates the first reference pattern of the reference pattern module.The beam splitter also receives the second beam of light and to splitthe second beam of light such that a first portion of the second beam oflight radiates the second overlay measurement pattern at the secondlocation of the substrate and a remaining second portion of the secondbeam of light radiates the second reference pattern of the referencepattern module. The stage controller and the layout position controllermove the substrate and the reference pattern module such that the firstand second portions of the first beam of light simultaneously radiatethe first overlay measurement pattern and the first reference patternand the first and second portions of the second beam of lightsimultaneously radiate the second overlay measurement pattern and thesecond reference pattern. In an embodiment, the diffracted light fromthe first reference pattern and the first overlay measurement patternare respectively reflected back from the reference pattern module andthe substrate. The beam splitter combines the diffracted light from thefirst overlay measurement pattern and the first reference pattern andproduces the first combination of diffracted light and sends the firstcombination of diffracted light to the one or more light detectors ofthe optical system. The diffracted light from the second referencepattern and the second overlay measurement pattern are respectivelyreflected back from the reference pattern module and the substrate. Thebeam splitter also combines the diffracted light from the second overlaymeasurement pattern and the second reference pattern and produces thesecond combination of diffracted light and sends the second combinationof diffracted light to the one or more light detectors of the opticalsystem. In an embodiment, the one or more light sources of the opticalsystem are coherent light sources.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method comprising: disposing a referencepattern module over a substrate, the substrate comprising a firstoverlay measurement pattern in a first location and a second overlaymeasurement pattern separate from the first overlay measurement patternin a second location, wherein the reference pattern module comprises afirst reference pattern and a second reference pattern separate from thefirst reference pattern; creating at least a first partial overlap ofthe first reference pattern with the first overlay measurement patternunder the reference pattern module; concurrently with creating the firstpartial overlap, creating at least a second partial overlap of thesecond reference pattern with the second overlay measurement patternunder the reference pattern module; determining a first overlay errorbetween the first reference pattern of the reference pattern module andthe first overlay measurement pattern of the substrate; determining asecond overlay error between the second reference pattern of thereference pattern module and the second overlay measurement pattern ofthe substrate; and determining a total overlay error between the firstand second overlay measurement patterns of the substrate based on thefirst and second overlay errors.
 2. The method of claim 1, wherein thefirst overlay measurement pattern is included in a first layout patternthat is in a first layer of the substrate and the second overlaymeasurement pattern is included in a second layout pattern that is in asecond layer of the substrate different from the first layer, andwherein an overlay error between the first and the second layoutpatterns is determined based on the total overlay error.
 3. The methodof claim 2, wherein the determining the overlay error between the firstand the second layout patterns comprises determining an algebraic sum ofthe first and second overlay errors.
 4. The method of claim 1, whereinthe determining the first overlay error comprises: applying a first beamof light over the first partial overlap of the first reference patternand the first overlay measurement pattern; and analyzing diffractedlight from the first overlay measurement pattern and the first referencepattern to determine the first overlay error.
 5. The method of claim 4,wherein the determining the second overlay error comprises: applying asecond beam of light over the second partial overlap of the secondreference pattern and the second overlay measurement pattern; andanalyzing diffracted light from the second overlay measurement patternand the second reference pattern to determine the second overlay error.6. The method of claim 5, wherein the analyzing the diffracted lightcomprises determining an intensity difference between positive andnegative first order diffracted light.
 7. The method of claim 1, furthercomprising: prior to creating the first partial overlap, generating thefirst reference pattern and the second reference pattern of thereference pattern module, wherein the first reference pattern has afirst pitch equal to a pitch of the first overlay measurement pattern ofthe substrate, and wherein the second reference pattern has a secondpitch equal to a pitch of the second overlay measurement pattern of thesubstrate.
 8. The method of claim 7, wherein: the first referencepattern of the reference pattern module comprises a first plurality ofthird sub-patterns extending in a first direction and being arranged ina second direction crossing the first direction, and a second pluralityof third sub-patterns extending in the first direction and beingarranged in the second direction, wherein the first plurality of thirdsub-patterns and the second plurality of third sub-patterns are arrangedwith an equal distance D3 at opposite sides of a third central lineextending in the first direction; and the first overlay measurementpattern of the substrate comprises a third plurality of firstsub-patterns extending in the first direction and being arranged in thesecond direction crossing the first direction, and a fourth plurality offirst sub-patterns extending in the first direction and being arrangedin the second direction, wherein the third plurality of firstsub-patterns and the fourth plurality of first sub-patterns are arrangedwith an equal distance D1 at opposite sides of a first central lineextending in the first direction, wherein when the first referencepattern of the reference pattern module is disposed over the firstoverlay measurement pattern of the substrate and the first central lineand the third central line overlap, the first plurality of thirdsub-patterns of the first reference pattern of the reference patternmodule has an offset d=D1−D3 with the third plurality of firstsub-patterns of the first overlay measurement pattern of the substrateand the second plurality of third sub-patterns of the first referencepattern of the reference pattern module has an offset −d=D3−D1 with thefourth plurality of first sub-patterns of the first overlay measurementpattern of the substrate.
 9. The method of claim 8, wherein thedetermining the first overlay error comprises: applying a first beam oflight over the first partial overlap of the first overlay measurementpattern and the first reference pattern; analyzing a first diffractedlight from the first plurality of third sub-patterns of the firstreference pattern and the third plurality of first sub-patterns of thefirst overlay measurement pattern to determine a first asymmetryfunction AS1 based on positive and negative first order diffraction ofthe first diffracted light; analyzing a second diffracted light from thesecond plurality of third sub-patterns of the first reference patternand the fourth plurality of first sub-patterns of the first overlaymeasurement pattern to determine a second asymmetry function AS2 basedon positive and negative first order diffraction of the seconddiffracted light; and determining the first overlay error between thefirst reference pattern of the reference pattern module and the firstoverlay measurement pattern of the substrate as:${d( \frac{{AS1} + {{AS}\; 2}}{{AS1} - {{AS}\; 2}} )}.$
 10. Amethod comprising: performing a first analysis of a first combination ofdiffracted light received from a first reference pattern of a referencepattern module and received from a first overlay measurement pattern ina first location of a first layer of a substrate to determine a firstoverlay error between the first reference pattern of the referencepattern module and the first overlay measurement pattern of thesubstrate; performing a second analysis of a second combination ofdiffracted light received from a second reference pattern of thereference pattern module and received from a second overlay measurementpattern in a second location of a second layer of the substrate todetermine a second overlay error between the second reference pattern ofthe reference pattern module and the second overlay measurement patternof the substrate; and determining a total overlay error between thefirst and second overlay measurement patterns of the substrate based onthe first and second overlay errors.
 11. The method of claim 10, whereinthe reference pattern module is disposed in parallel over the substrate.12. The method of claim 10, wherein the first overlay measurementpattern and the second overlay measurement pattern are in differentlayers of the substrate.
 13. The method of claim 10, wherein thereference pattern module is disposed perpendicular to the substrate, andthe method further comprises: projecting a coherent beam of light to abeam splitter; configuring the beam splitter to direct a first portionof the coherent beam of light from the beam splitter to the firstreference pattern of the reference pattern module and to direct aremaining second portion of the coherent beam of light from the beamsplitter to the first location of the first layer of the substrate;combining by the beam splitter, diffracted light received from the firstreference pattern of the reference pattern module and received from thefirst overlay measurement pattern in the first location of the substrateto generate the first combination of diffracted light; directing, by thebeam splitter, the first combination of diffracted light received fromthe first overlay measurement pattern and received from the firstreference pattern to an optical system for detection and analysis; andanalyzing positive and negative first order diffractions of the firstcombination of diffracted light by an analyzer module coupled to orincluded in the optical system to determine the first overlay error. 14.The method of claim 13, further comprising: configuring the beamsplitter to direct the first portion of the coherent beam of light fromthe beam splitter to the second reference pattern of the referencepattern module and to direct the remaining second portion of thecoherent beam of light from the beam splitter to the second location ofthe second layer of the substrate; combining by the beam splitter,diffracted light received from the second reference pattern of thereference pattern module and received from the second overlaymeasurement pattern in the second location of the substrate to generatethe second combination of diffracted light; directing, by the beamsplitter, the second combination of diffracted light received from thesecond overlay measurement pattern and received from the secondreference pattern to the optical system for detection and analysis; andanalyzing positive and negative first order diffractions of the secondcombination of diffracted light by the analyzer module to determine thesecond overlay error.
 15. A method of overlay error measurement,comprising: disposing a reference pattern module over a substrate, thesubstrate comprising a first overlay measurement pattern in a firstlocation and a second overlay measurement pattern separate from thefirst overlay measurement pattern in a second location; generating inthe reference pattern module a first reference pattern and a secondreference pattern separate from the first reference pattern; irradiate,by a first beam of light, the first reference pattern of the referencepattern module and the first overlay measurement pattern and irradiate,by a second beam of light, the second reference pattern of the referencepattern module and the second overlay measurement pattern; receiving afirst combination of diffracted light received from the first referencepattern of the reference pattern module and the first overlaymeasurement pattern in the first location of the substrate; receiving asecond combination of diffracted light received from the secondreference pattern of the reference pattern module and the second overlaymeasurement pattern in the second location of the substrate; performinga first analysis of the first combination of diffracted light todetermine a first overlay error between the first reference pattern ofthe reference pattern module and the first overlay measurement patternof the substrate; performing a second analysis of the second combinationof diffracted light to determine a second overlay error between thesecond reference pattern of the reference pattern module and the secondoverlay measurement pattern of the substrate; and determining a totaloverlay error between the first and second overlay measurement patternsof the substrate based on the first and second overlay errors.
 16. Themethod of claim 15, wherein the first overlay measurement pattern isincluded in a first layout pattern in a first layer of the substrate andthe second overlay measurement pattern is included in a second layoutpattern in a second layer of the substrate different from the firstlayer, the method further comprising: determining an overlay errorbetween the first layout pattern and the second layout pattern of thesubstrate based on the first overlay error and the second overlay error.17. The method of claim 15, wherein the first beam of light is acoherent beam of light and the second beam of light is a coherent beamof light.
 18. The method of claim 15, further comprising: disposing thereference pattern module in parallel over the substrate.
 19. The methodof claim 18, further comprising: moving the reference pattern module inparallel with the substrate to produce at least a first partial overlapof the first reference pattern above the substrate with the firstoverlay measurement pattern in the first location of the substrate andto produce at least a second partial overlap of the second referencepattern above the substrate with the second overlay measurement patternin the second location of the substrate; producing the first beam oflight over the first partial overlap; and producing the second beam oflight over the second partial overlap.
 20. The method of claim 18,further comprising: determining the first overlay error based onpositive and negative first order diffractions of the first combinationof diffracted light; and determining the second overlay error based onpositive and negative first order diffractions of the second combinationof diffracted light.